Device for radiating circularly polarized waves



Sept. 16, 1952 ALFORD 2,611,087

DEVICE FOR RADIATING CIRCULARLY POLARIZED WAVES Filed Jan. 29, 1946 10 If b ..i 1. I

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nvvs/vron ANDREW ALFORD BY 7 m 9.1442

A T TORNE Y Patented Sept. 16, 1952 DEVICE FOR RADIATING CIRCULARLY POLARIZED WAVES Andrew Alford, Cambridge, Mass assignor to the United States of America as represented by the Secretary of War Application January 29, 1946, Serial No. 644,175

8 Claims. 1

This invention relates to the propagation of polarized waves of radio frequency electromagnetic energy and to means for producing circularly polarized Waves. It is more particularly directed to a device wherein plane-polarized radio frequency energy from a hollow pipe wave guide is changed to circularly polarized energy for radiation.

As is well known, the phenomenon known as circular polarization is set up when two plane polarized waves of equal amplitude have their planes of polarization perpendicular to each other and are in time quadrature (polarization being defined in the sense used in theradio art rather than in the optical sense, and referring herein to the direction of the electric vector rather than that of the magnetic vector). This invention contemplates a simple and novel means of attaining circular polarization by means of suitable wave guide transition sections which will set up a difierence in electrical path length between the two components of plane polarized waves.

It is one of the objects of the present invention to provide means for producing electromagnetic waves of circular polarization from linearly polarized plane waves.

It is another object of the invention to provide means for transition between plane and circularly polarized electromagnetic waves.

It is still another object of the invention to provide, in a wave guide transmission line, Wave guide sections so dimensioned that a transition to circularly polarized waves from linearly polarized waves, is effected.

Another object of the invention is to provide a horn radiation system wherein a tapered section of wave guide is utilized to resolve the plane polarized wave from a conventional wave guide feed line into two mutually perpendicular components and wherein a section of rectangular wave guide is utilized to change the relative time phase of these components to 90 before radiation, from the flared portion of the horn, as a circularly polarized wave.

Other objects and advantages of the invention will become apparent from the following description with reference to the accompanying drawings, in which:

Fig. 1 is a perspective view of a horn radiating element having a wave guide feed and transition sections according to the invention;

Fig. 2 is a sectional view along the line 2-2 Of Fig. 1; 1

Fig. 3 is a sectional view along the line 3-3 01' Fig. 1; and

2 Fig. 4 is a sectional view along the line 4-4 of Fi 1.

In the drawings, the horn radiating element is generally designated l0 and comprises a flared portion H, a rectangular wave guide portion [2 and a tapered wave guide portion l3 arranged for transmission of energy Waves therethrough. Radio frequency energy, such as energy in the microwave range of frequencies (i. e., having wavelengths of the order of centimeters) is supplied to horn It) by means of a conventional rectangular wave guide 14 communicating with one end (as shown, the lower end) of tapered portion 13.

It will be understood that the term rectangu lar as applied to the cross-section of wave guide portions l4 and wave guide 12 is intended to include an "effective rectangular section such as an elliptically shaped section which maybe produced by rounding the corners of a rectangularly shaped cross-section.

The cross-sectional dimensions of Wave guide portion H are preferably larger than the corresponding dimensions of wave guide [4. Also portion 12 is angularly displaced about the longitudinal axis of horn ID with reference to Wave guide 14 so that the plane of the wider wall b or the major axis of its cross-section is at an angle of substantially 45 to the plane of wider wall b or of the major axis of the cross-section of wave guide [4. 1

To effect the transition between portion [2 and wave guide M, the tapered portion l3 preferably comprises eight triangularly shaped sections 15 and 1-6. The bases of the four sections 15 substantially form a rectangle at the lower end of portion 13 of substantially the same cross-sectional dimensions as that of wave guide I4, to the upper end of which the bases are adapted to be attached. Similarly, the bases of the four triangular sections [6 substantially form a rectangle at the upper end of tapered portion [3 having substantially the same dimensions as the lower end of wave guide portion [2 to which the portion I3 is adapted to be attached. The triangular sections I5 are joined along their sides to the sides of triangular sections IS with the apices of sections [5 being at the corners of the rectangle formed by the bases of sections [6 and the apices of sections l6 meeting the corners of the rectangle formed by the bases of sections l5. Thus portion. [3 affords a tapered transition, and permits energy to pass, from wave guide M to wave guide i2. It will be noted that the planes of sections 15 are preferably substantially at an angle of 45 to the planesof the corresponding ing along the tapered portion l3, the. electricvector E is directed along the diagonal of the cross-section of wave guide portion [2. By the time the wave arrives at the junction of tapered portion l3 and wave guide portion |2,the electric vector is eifectively resolved into two mutually perpendicularcomponents; One; compo nent is parallel to side b and theother is parallel to side a of wave guide portion I2; By mar: ing the cross-sectional dimensions a and b both greater than a half wavelength of the'energy in space, it is possible for the two-component waves tojp'ropagate along the length of wave guide porhon |-2 Both component waves are of transverse electrical type and each behaves in much the same anner asa transverse electrical wave in a com ventional wave guide. The phase velocities at Whichthe two-component waves are propagating are different from one another when dimensions rectangular wave guide coupled to said radiating means and having both of its cross-sectional dimensions greater than a half wavelength of the energy to be radiated, said cross-sectional dimensions being diiferent from each other, a second rectangular wave guide for feeding said first wave guide, said first waveguide being .oriented with its walls at substantially 45 with respect to the walls of said second wave guide, and a transition portion coupling and matching said wave guides together, whereby plane polarized waves in said second wave guide are divided in said first wave guide into a first component polarized perpendicularly to the narrow walls ther'eof and a second component polarized perpendicularly to the wide walls thereof, said first and. second components having substantially equal amplitudes, said first wave guide having a dand b are-unequal; Because of this difference in velocities, there is a progressively increasing phase difference between the two electric vectors whichare at right angles to each other in space. After-thetwo=component waves have propagated ever a suitameoista ce, L, the. time phase dis.- tance between the two electric vectors becomes 7 equal to 90; so that these vectors are not only in space quadrature but also in time quadrature thereby resulting in circularly polarized energy waves. 1

This is the case at the bottom of the flared portion ll. The aperture of the flare l I maybe ma ds approximately square and the flar itself is usually fairly short, so that the difie'rence. in phase does not continue to increase within the flare. The result is that the flared portion ll acts merely as a transformer :or as animpedance matching section between the rectangular guide and space, reducing the reflection at the end of the rectangular guide to a small value. When the flare is made gradual, further small phase differentiation may occur within the flare. This, however, may be allowed for by making the length of the main phasing section 12 somewhat shorter.

While the invention as hereinbefore described has been particularly directed to .a horn radiating element, it will be understood that the invention is not limited thereto. It will :be obvious that instead of terminating wave guide l2 a horn, any other suitable termination may be utilized; also the portions I2 and 13 may form a transition .portion in a transmission :line wherein circular polarization is desired.

While there has been described what is at present considered the, preferred embodiment of the invention, it will be obvious to those skilled in the art that various changes and modificat'mns-cmay be made therein without departing fiomzidiec'mvention.

bdwhattiisacia'zmed is:

oilt lAeflHVgcevm! radiating circularly polarized electromagnetic between comprising radiating mansnmmmmasmmu, wave guide, a first length such that said first component of said waves is delayed substantially electrical degrees relative 'the second component of said waves.

2. A device for obtaining a pair of electromagnetic waves polarized perpendicularly to one another comprising a first rectangular "wave guide having both of its cross-sectionaldimensions greater than a half wavelength of the' energy to be radiated, a secondrectangul'ar wave guide for feeding said first Wave guide, said second wave guide having-its walls oriented at. an oblique angle with respect to the walls of said first wave guide, and-a transition portion coupling and matching said wave guides together, whereby plane polarized waves in said vsecond wave guide. are divided in said .first wave. guide into a first component polarized perpendicularly to one pair of opposite walls thereof. and a sec-- ond component polarized perpendicularlyto the ether pair of opposite wallsithereof.

3. A device for radiating circularly polarized electromagnetic waves means adapted to be fed by a wave guide, a first rectangular wave guide coupled to said radiating means and having :both of its cross sectional dimensions greater than a half: wavelength {of the energy to be radiated, said cross-sectional dimensions being diiferentfrom each other, a second rectangular wave guide for feeding said first wave guide and. oriented with its :walls at.45.i with respect to the walls of said first wave guide, and atransition portion. coupling and matching said wave guides together, said transition portion including eight triangular portions four positioned with their bases coupled one to each of the walls of said first wave guide and with their apices coupled one to eachv of the corners of said. second wave guide, the remaining four of, said triangular portions having their bases coupled one to each of the walls of said second wave guide and their ,apices coupled one to each of the. cormm of said first wave guide, whereby plane polarized, waves in said second wave guide are divided in said first wave guide into a first component polarized perpendicularly to the narrow walls thereof and a second component polarized perpendicularly to the wide walls thereof, said first and second components having substantially equal amplitudes, said first Wave guide having a length such that said first component of said waves is delayed substantially 90 electrical de grees relative to said second component ofsaidother from a plane polarized wave comprising a comprising radiating V rectangular wave guide for propagating plane polarized waves and an additional wave guide coupled to said rectangular wave guide and including eight triangular portions four of which are positioned with their bases coupled one to each of the walls of said rectangular wave guide at an end thereof, the apices of said four triangular portions being positioned in a plane and defining the four corners of a rectangle both 01: whose cross-sectional dimensions are greater than a half wavelength of the electromagnetic waves and whose sides are oriented at 45 with respect to the walls of said Wave guide, the remaining four of said triangular portions being positioned with their apices coupled one to each of the four corners of said rectangular wave guide and with their bases positioned each along one of the sides of said rectangle.

5. A device for producing elliptically polarized electromagnetic waves comprising a first rectangular wave guide having both of its cross-sectional dimensions greater than a half wavelength of the energy to be radiated, said crosssectional dimensions being different from each other, a second rectangular wave guide for feeding said first wave guide, said second wave guide having its walls oriented at an oblique angle with respect to the walls of said first wave guide, and a transition portion coupling and matching said wave guides together, whereby plane polarized waves in said second wave guide are divided in said first wave guide into a first component polarized perpendicularly to the narrow walls thereof and a second component polarized perpendicularly to the wide Walls thereof, said first wave guide having a length such that said first component of said waves is delayed substantially 90 electrical degrees relative to the second component of said waves, whereby the waves emanating from the end of said first wave guide are elliptically polarized.

6. A device according to claim 5, further including radiating means coupled to said end of said first wave guide for radiating the waves emanating therefrom.

ANDREW ALFORD.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,129,669 Bowen Sept. 13, 1938 2,129,714 Southworth Sept. 13, 1938 2,255,042 Barrow Sept. 9, 1941 2,317,464 Katzin Apr. 27, 1943 2,412,320 Carter Dec. 10, 1946 2,416,675 Beck et a1. Mar. 4, 1947 2,425,345 Ring Aug. 12, 1947 2,438,119 Fox Mar. 23, 1948 

